1. The problem statement, all variables and given/known data

In exercising, a weight lifter loses 0.150 kg of water through evaporation, the heat
required to evaporate the water coming from the weight lifter's body. The work done
in lifting weights is 1.40x10^{5} J. (a) Assuming that the latent heat of vapourisation
of perspiration is 2.42x10^{6} Jkg^{-1}, find the change in the internal energy of the weight lifter.

2. Relevant equations

Q = mL

Δu = Q - w

3. The attempt at a solution

Q = mL
= 0.15 * 2.42x10^{6}
= 363000 J

This is the amount of energy required to vapourise the perspiration.

Δu = Q - w

= 363000 - 1.40x10^{5}

= 223000 J

Is this correct?

I was half expecting my answer to be negative since the weight lifter will have less energy after lifting weights, but I suppose it makes sense that he would also get hot which is what internal energy measures.

ETA The next part of the question goes on to say this;

Which supports my feeling that i'm wrong...

One thought i'm having is that since the energy required to vapourise the perspiration is coming from the body, I should be giving it as a negative figure.

Q in the first law expression is defined as the heat gained by the body. In your example, Q should be negative because evaporation of sweat causes the body to lose heat.